1. Field of the Invention
This invention is related to a process for the preparation of glycol aldehyde, and more particularly, is related to the preparation and purification of glycol aldehyde which is subsequently hydrogenated to ethylene glycol; the process proceeding via the catalytic reaction of formaldehyde, carbon monoxide and hydrogen and utilizing a novel class of lipophilic rhodium-phosphine-amide catalysts and an effective solvent mixture. The process features high reactant conversions, selectivities, product and recyclable catalyst recoveries.
2. Description of the Prior Art
Glycol aldehyde is well known as a valuable intermediate in a variety of organic reactions, and is particularly useful as an intermediate in the production of ethylene glycol.
Ethylene glycol is well known as a valuable industrial chemical having a wide variety of uses, such as a coolant, an anti-freeze, a monomer for polyester production, and an industrial solvent.
The reaction of formaldehyde with carbon monoxide and hydrogen at elevated temperatures and superatmospheric pressures in the presence of a variety of catalysts is a well known reaction and yields glycol aldehyde, as well as methanol and lesser amounts of polyhydroxy compounds, which must be separated from the glycol aldehyde. U.S. Pat. No. 3,920,753 discloses the production of glycol aldehyde from the reaction of formaldehyde, carbon monoxide and hydrogen in the presence of a cobalt catalyst under controlled reaction conditions, however, the process produces relatively low yields of product. Japanese Pat. No. J57-118,527 describes the production of glycol aldehyde by using a ruthenium catalyst system. European Patent Application No. 002,908 describes a process for the production of glycol aldehyde from the reaction of formaldehyde, in the presence of a rhodium-triphenyl-phosphine ligand catalyst, with carbon monoxide and hydrogen, in a tertiary amide solvent. This reference further suggests that the glycol aldehyde product is preferably extracted from a water-immiscible hydroformylation solvent. However, the proposed method suffers from the drawback of limiting the choice of hydroformylation solvent to the class of water immiscible solvents, whereas the most effective hydroformylation solvents, such as acetonitrile, are very water soluble. Furthermore, when extracting glycol aldehyde with an aqueous extractant, even when using a water-immiscible solvent, a substantial amount of the expensive rhodium catalyst migrates into the water phase and is lost, thereby decreasing both the amount and the resultant activity of the remaining catalyst.
U.S. Pat. No. 4,291,179 describes a similar reaction for the production of acetaldehyde in which trifluoroacetic acid is added to produce ethylene glycol. U.S. Pat. No. 4,356,332 describes the preparation of ethylene glycol from the reaction of synthesis gas and formaldehyde, using a rhodium or cobalt catalyst in the presence of a substantially inert oxygenated hydrocarbon solvent. European Patent Application No. 82/200,272.1 describes a process for the preparation of glycol aldehyde which comprises reacting formaldehyde, hydrogen and carbon monoxide in the presence of either a rhodium or cobalt containing catalyst precursor, together with a strong protonic acid, a tertiary amide solvent and a triaryl phosphine. U.S. Pat. No. 4,200,765 discloses a process of preparing glycol aldehyde involving reacting formaldehyde, carbon monoxide, and hydrogen in a tertiary amide solvent in the presence of a catalytic amount of rhodium in complex combination with carbon monoxide, using triphenylphosphine as the preferred catalyst promoter. U.S. Pat. No. 4,405,814 discloses a similar process for the production of glycol aldehyde, incorporating a tertiary organo phosphorous or arsenic moiety into the rhodium catalyst together with a basic organo amine. U.S. Pat. No. 4,405,821 discloses still another similar process involving carrying out the reaction in the presence of a glycol aldehyde yield enhancing phosphine oxide.
A major flaw in the prior art processes utilizing transition metal-phosphine catalysts has been the inability to recover a satisfactory amount of the expensive metal, e.g., rhodium, catalyst after the hydroformylation reaction, thus frustrating the desire to recycle and reuse the catalyst. In the propylene hydroformylation of n-butyraldehyde large excesses of triarylphosphine (U.S. Pat. No. 4,277,627) coupled with the introduction of small quantities of diarylalkylphosphine (U.S. Pat. No. 4,260,828) were used to stabilize the resulting rhodium compounds. However, in the instant formaldehyde hydroformylation process such an excess of either alkyl or arylphosphine is not feasible, due to the resulting substantial increase in methanol selectivity at the expense of glycol aldehyde selectivity when operating with an increased phosphine concentration, i.e., above a three to one phosphine to rhodium ratio.
The prior art processes for the production of glycol aldehyde have also produced a wide mixture of undesired reaction products, such as polymeric formaldehyde and methanol. Consequently, time-consuming separation procedures are required, a fact that the patent literature tends to gloss over, as well as a corresponding reduction in the amount of desired product formed. Additional problems involved in the hydroformylation of formaldehyde to glycol aldehyde are the rapid decline in activity of the transition metal catalyst, the presence of competing aldol condensation and acetal formation reactions hampering the separation of the product, and the formation of catalyst-poisoning amines.
In copending U.S. Patent Application Ser. No. 508,704, filed June 28, 1983, several of these problems were solved by the utilization of a novel class of phosphine-amide catalysts having the formula: MX.sub.x (CO).sub.y [P(R.sub.1).sub.2 R.sub.2 C(O)--NR.sub.3 R.sub.4 ].sub.z, wherein M is an element selected from the group of rhodium, cobalt, and ruthenium, preferably rhodium; X is an anion, preferably a halide, a pseudohalide, a hydride or a deprotonated strong carboxylic acid; P is phosphorous; R.sub.1 is an aromatic or aliphatic group of 1-20 carbon atoms, preferably aromatic; R.sub.2 is an organo group containing from 0 to 20 carbon atoms of either aliphatic or aromatic nature and may also include oxygen, nitrogen or sulfur atoms, which atoms may be directly bonded to the amide C(O)N carbon, or nitrogen; R.sub.3 and R.sub.4 are each aliphatic or aromatic groups containing from 1 to 50 carbon atoms; the resultant compound being characterized by the absence of hydrogen on the amide nitrogen atom and the additional limitation that if R.sub.2 is bonded to the amide nitrogen, then either R.sub.3 or R.sub.4 is bonded to the amide carbon; x ranges from 0 to 3, y ranges from 1 to 5, and z from 1 to 4. However, the most preferred rhodium-phosphine-amide catalysts cited in this formaldehyde hydroformylation system are ineffective as catalysts for the subsequent glycol aldehyde hydrogenation to ethylene glycol. Consequently, it becomes essential for commercial success to be able to extract the glycol aldehyde from the reaction mixture and either subsequently hydrogenate it to ethylene glycol in the presence of an effective catalyst, or utilize it in another manner. However, we have discovered that the phosphine-amide catalysts have a strong tendency to migrate into the glycol aldehyde product phase and cannot be readily recovered, thereby ruining the economics of the resulting process, which requires an active recyclable catalyst.
Thus, it is an object of this invention to provide an improved process for the hydroformylation of glycol aldehyde and its subsequent hydrogenation to ethylene glycol which has high conversions and selectivities, from the reaction of formaldehyde, carbon monoxide and hydrogen feedstocks.
It is another object of this invention to provide a process wherein the glycol aldehyde and the transition metal-phosphine-amide catalyst can be easily separated and extracted or recycled from the reaction product mixture in an effective industrial operation.
It is still another object of this invention to develop a process wherein the hydroformylation catalyst is substantially prevented from migrating into the glycol aldehyde product phase during separation, thus preventing the loss of the expensive catalyst.
It is still another object of this invention to provide a process for the hydroformylation of formaldehyde which is able to recycle the rhodium catalyst a substantial number of times without suffering a substantial loss in catalyst activity.